The present invention relates generally to field effect transistor (FET) amplifiers, and specifically to a protection circuit which provides bias, input matching, and limiting to a FET amplifier on a gallium arsenide (GaAs) microwave monolithic integrated circuit (MMIC).
The Global Positioning System (GPS) is used by a variety of users for determining the geodetic location of objects using signals received from GPS satelliles. Currently, there is a need to improve GPS receivers for a number of these users. This improvement includes a reduced size in GPS user sets to less than 100 cubic centimeters, and a reduced power consumption to 1.7 watts. This goal is remarkable in that less than a decade ago, first generation GPS sets were two or more cubic feet in volume and weighed upwards of 100 pounds.
The goal of reducing the volume and power of GPS receivers is attainable through the use of GaAs microwave monolithic integrated circuits, and the low noise amplifier (LNA) of the present invention is intended for use with GPS receivers. This task of providing a low noise amplifier with a limiting circuit to protect the amplifier from high voltages is alleviated, to some degree, by U.S. Pat. No. 4,011,518 issued to Irvine et al on 8 Mar. 1977, the disclosure of which is incorporated herein by reference. The Irvine reference discloses a GaAs field effect transistor (FET) amplifier circuit which provides constant gain under varying temperatures.
GaAs semiconductive devices help attain the goal of reduced volume. However, the limiting circuits of the prior art commonly requires extra components, space and power on the integrated circuit. From the foregoing discussion, it is apparent that there currently exists the need for a protection circuit which reduces the comonents, space and power for FETs which provide limiting, bias and input matching to the LNA. The present invention is intended to satisfy that need.